The Local Bubble is thought to have been caused my multiple supernovae. See e.g. this 2002 paper: https://arxiv.org/abs/astro-ph/0205128v2 https://arxiv.org/abs

The Local Bubble is thought to have been caused my multiple supernovae. See e.g. this 2002 paper: https://arxiv.org/abs/astro-ph/0205128v2 https://arxiv.org/abs/astro-ph/0205128v2 Edit: Here's a more recent paper - https://link.springer.com/referenceworkentry/10.1007%2F978-3-319-20794-0_14-1 https://link.springer.com/referenceworkentry/10.1007%2F978-3... : > "More detailed models for the origins of the Local Bubble have found that it requires anywhere from 3 (Smith and Cox 2001) to 20 (Fuchs et al. 2006) SNe to create a bubble with the correct characteristics in terms of size, pressure, and emission characteristics."